Generally, respective electrodes (e.g., a control electrode, an accelerating electrode, and a focus electrode) of an in-line electron gun are placed to be apart from one another by a predetermined distance to be perpendicular to a path through which electron beam passes, so that the electron beam originated from a cathode is controlled in regular intensity and shaped to reach a screen.
As illustrated in FIG. 1, a general color picture tube having such an electron gun includes cathodes 3 separated from one another for emitting electron beams 13, and a control electrode 4 for controlling the electron beams 13 from the cathodes 3. An accelerating electrode 5 directs to accelerate thermoelectrons gathered around the surface of the cathodes 3 while maintaining a regular distance from the control electrode, and first and second accelerating/focusing electrodes 6 and 7 focus the electron beams 13 having passed through the accelerating electrode 5 onto a phosphor screen 11. In addition to these, the color picture tube has a shield cup 8 attached with bulb spacers 9 placed on the upper portion of the first and second accelerating/focusing electrodes 6 and 7, heaters 2 for generating heat by means of a power from stem pins 1, a mask 10, a deflection yoke 12, and a neck 14.
The operation of the color picture tube constructed as above will be briefly described.
Once the heater 2 installed within the cathode 3 generates heat by receiving the power via the stem pin 1, the cathode 3 emits electrons, and the control electrode 4 controls the path of the electron beam 13 produced by gathering the electrons. The controlled electron beam 13 is accelerated by the accelerating electrode 5, focused after passing through the first and second accelerating/focusing electrodes 6 and 7 which form a main lens, and then passes through the mask 10 installed to the inner surface of the phosphor screen 11 to collide with phosphors on the phosphor screen 11. The collision of the electron beam radiates light to allow the color picture tube to display a picture.
In the general color picture tube, the structure of the triode of the conventional in-line electron gun is illustrated in FIG. 2.
Here, the accelerating electrode 5 has by an embedded regressive slot 15 therein which is wider in the horizontal direction than in the direction perpendicular to the horizontal direction with respect to holes.
FIG. 3 is a simulation modeling of electric field distribution and emission of the electron beam in the triode shown in FIG. 2. The electron beam 13 emitted from the cathode 3 presents a crossover phenomenon that the electron beam 13 attracts onto a certain point to be reradiated by the influence of an electrostatic lens formed between the accelerating electrode 5 and control electrode 4. It is considered that an equipotential line of the accelerating electrode 5 results in the crossover phenomenon by focusing to attract the emitted electron beam 13 after passing through the control electrode 4.
After focusing a crossover point 41 as described above, the electron beam 13 is focused and diverged by a lens formed by the accelerating electrode 5 to advance toward the main lens.
In association with the structure, however, the regressive slot 15 in the accelerating electrode 5 thickens the accelerating electrode in horizontal direction when compared with that in the vertical direction to force the horizontal diverging angle to be wider than the vertical diverging angle of the electron beam 13, thereby forming a horizontally-elongated electron beam.
The horizontally-elongated electron beam serves to decrease the focusing of the vertical electron beam and prevent the collision and increased repulsion among the electrons in the electron beam by a magnetic field of the deflection yoke 12.
However, in the conventional in-line electron gun, since the crossover point is formed at high speed after emitting the electron beam, the divergence force of the electron beam is abruptly increased in the overall area of the high current region. Therefore, the electron beam raises spherical aberration which is caused by the different reflective index between the center and periphery in the main lens portion to induce a problem in the focus characteristic. Also, the slot for forming the horizontally-elongated electron beam is liable to produce eccentricity and deformation during the fabrication process thereof which is very demanding operation.
Furthermore, the focusing force of peripheral beam toward the central beam is changed resulting from the voltage variation of the first accelerating/focusing electrode to involve a problem in the fabricating operation as well as degrade quality characteristic.